I. Field of the Invention
The present invention relates to an apparatus and method for sorting mixtures of materials into constituent parts and then recombining the constituent parts into mixtures of a desired ratio. In its simplest form, the apparatus of the present invention uses two or more density separators, a separate control valve associated with each density separator, a separate differential pressure sensor associated with each density separator and at least two splitters, all operated under program control, to first divide a mixture of minerals into constituent parts and then use the constituent parts to create an end product of a predetermined composition. The program used to control the equipment can, of course, be altered to change the composition of the end product.
II. Description of the Related Art
It is well known in the construction arts that the nature and durability of various construction materials which incorporate sand or other granular mineral materials vary based upon the particle size distribution of the granular material used. Thus, various techniques have been employed in the prior art to treat raw sand and other granular materials, the constituent parts of which are of an unknown and non-uniform size, to obtain at least one end product which meets the desired specification. The same techniques have been employed with other particulate materials. Prior art techniques often incorporate the use of one or more density separators which divide a source material into a relatively coarse underflow fraction and a relatively fine overflow fraction. The density separators typically include equipment, such as a valve, for varying the size of the material as required by varying the flow rate of the underflow fraction in relation to the pulp density within the density separator. By using a density separator to separate the raw material into two constituent parts, stockpiles of the constituent parts can be created.
To meet the specification requirements for a particular mixture, a desired blend of the two constituent products can be created. In the prior art, this has typically been done by storing the constituent parts separately in bins and then drawing from the bins whatever relative weights of materials are required for the desired blending. This technique suffers from several disadvantages. First is the cost of the weigh scales and the bins. Second is the space required for such equipment and storage of the constituent parts. Third is the lack of uniformity of blending produced with such equipment due to unpredictable flow rates and non-uniform moisture content of the raw materials used.
U.S. Pat. No. 6,085,912 which issued on Jun. 11, 2000 to Earl L. Hacking, Jr. and Thomas A. Swaninger discloses a system that solves many of the problems outlined in the prior art. The invention disclosed in the '912 patent is directed to an apparatus for separating a first mixture of substantially granular materials into its constituent parts and then remixing constituent parts to achieve a second mixture having a desired composition. This apparatus includes a first density separator which divides the first mixture into first and second flow streams. The first flow stream consists of a first material having a first controlled density or size. Likewise, the second flow stream consists of a second material having a second controlled density and size less than the first controlled density or size. This apparatus also includes a control valve for regulating the exit of the first flow stream from the density separator and for controlling the division of the first mixture into first and second flow streams by the first density separator. A first sensor is also provided. This sensor generates an electrical signal indicative of the rate at which material within the first flow stream is exiting the density separator. The system also includes a second sensor which provides a signal indicative of the pulp density of the material within the first density separator. A splitter is associated with the first flow stream exiting the density separator for controlling the delivery of the material in that flow stream. A controller is also provided to respond in real time to signals provided by the sensors to automatically control the control valve and the splitter to produce an ingredient having a desired composition. The patent goes on to explain how ingredients created using this technique can be recombined to make desired products.
FIG. 1 of the '912 patent specifically shows how a pair of such density separators and splitters can be used in conjunction with other equipment to create at least six different constituent products.
The present invention represents an improvement over what is shown in U.S. Pat. No. 6,085,912. It provides greater flexibility in combining materials to achieve the precise end product desired without, at the same time, creating numerous other less desirable end products. Thus, the present invention improves on the efficiency achieved by the system shown in the '912 patent and also reduces the space required to produce a desired product.